>> This makes a big difference on some applications, on the order of 40% on both Atom and Core i7, as demonstrated by non-trivial benchmarks run by the x32 ABI developers.
> Where are you reading that 40%?
This is a pointer chasing benchmark where the entire data set consists of pointers, or hardly a realistic test case. It is furthermore an amazingly poorly written piece of software. In many places it needlessly uses global variables in inner loops, which can thwart compiler optimisations (particularly aliasing-based ones). It also uses 'long' exclusively where any sane programmer would use 'int', possibly leading to more expensive 64-bit operations being used where there really is no need.
Moreover, the website does not mention which compiler, let alone which compiler flags, were used, nor does it provide any raw numbers from the benchmark run. A lone percentage figure as presented there means absolutely nothing whatsoever.
Finally, out of all the spec2k modules, they chose to showcase only two, presumably because those two showed the most favourable results. The second one is 186.crafty, showing a meagre 3% improvement (4% on Atom). This leaves one wondering what the results of the remainder looked like. Something tells me they showed improvements of less than 3%, if any at all.